Harris, a first-term U.S. senator and former California attorney general, bashed Biden for his comments at a June 25 New York City fundraiser, at which he reminisced about the atmosphere of political fellowship when he was a senator in the 1970s and 1980s—comparing it to today’s climate, in which political rivals are considered “the enemy.”

At that event, Biden cited his ability to work with such staunch segregationists as Senator James Eastland (D- Mississippi), who Biden said was “one of the meanest guys I ever knew.”

“I was in a caucus with … Eastland,” Biden said and then, imitating a Southern accent, added that the senator “never called me ‘boy,’” a racial epithet used against black men (but not against Caucasians such as Biden).

At the end of her attack, she threw a curveball that knocked both Biden and the audience off their feet: ““There was a little girl in California who was part of the second class to integrate her public schools, and she was bused to school every day, and that little girl was me,” Harris said.

Biden called Harris’s blitzkrieg “a mischaracterization of my position across the board,” arguing, “I did not praise racists.”

As NBC news reported, the former vice president also reiterated the argument he has made in the past: that the federal government should not have been empowered to force schools to use busing as a means of desegregation..

By the end of the back and forth, the usually loquacious Biden cut himself off. “My time is up,” he said abruptly. “I’m sorry.”

“That was a brilliant debate performance,” Luntz said to CNBC of Harris. “She’s the winner of both nights.”

So, would Harris be the best adversary to Trump in a future debate?

“Don’t focus on the national numbers,” said Luntz, who refused to say which Democratic candidate would present the toughest challenge to Trump’s reelection campaign.At this point, it’s all about convincing primary voters in key early-voting states, the pollster said. “What really matters is Iowa, New Hampshire, South Carolina. ”